Session Border Controllers (SBCs) are maturing from a point product for securing SIP trunking and SIP protocol interworking into a critical component for providing communication solutions between different devices, networks, platforms, and applications.
In an ideal world, the industry would gravitate towards a common standard. While the industry is converging towards SIP as the common communications protocol for real-time media like voice and video, the number of codecs is diverging. Microsoft and Skype, for example, have their own proprietary codecs, along with a slew of new ones in the industry. These new codecs are used for cellular devices where bandwidth is at a premium, as well as high-definition audio and video conferencing for business communication where a "close to real life" experience is desired.
With SIP, the objective is for the end device to negotiate the codecs. This sounds good in theory, but in practice, because users are on different networks with different devices supported by different platforms, it is difficult for an end device to support all options. This is especially true when a mobile device with a small screen and limited CPU communicates with a high-end PC on a fast Internet connection. The video and the voice both must be transcoded in order for each user to have an optimal experience. This model also breaks down when conferencing in additional parties.
Since it is expensive and unrealistic for an end device to support all communication types, devices, standards and networks, SBCs are used to broker the communication. SBCs provide:
1) VoIP Security: NAT/PAT, Authentication, Logging, Encryption, DoS, …
2) SIP Protocol Interworking: SIP, SIP-T, SIP-I, H.323, TCP/UDP
3) Reporting: Billing, Utilization, Logging
4) Routing: Dialed Number, Origination Number, Network, CAC, Cost, Time, etc.
5) Troubleshooting: Ladder Diagrams, Protocol Decode, Media Capture
6) Media Interworking and Services:
* Transcoding--Going from one codec to another--G.711, G.729, G.722, iLBC, etc.
* Conferencing--Adding additional parties to an interaction
* Queuing – Putting an interaction on hold and play music or announcements
* Recording--Capturing the interaction for later playback
* Translation--Real- or semi-real time translation from one spoken language to another (future)
* DTMF & Fax--RFC 2833, T.38
* Voice Quality--Echo cancellation, gain normalization, background noise elimination
7.) Additional Call Data: Using Mime in the SDP to carry location and other communication information
8.) High Availability: Rerouting call traffic when a network or device slows or fails
9.) Management: Dial Plan, Load Balancing, Categorization, Provisioning
10.) Emergency Services: 911, CALEA
Organizations should plan on creating a layered security model for real-time applications. This is similar to IT data center models where multiple firewalls at different points within the DMZ provide layers of security, interworking, support, and reporting.
An SBC is used to transit each layer. This architectural model falls in line with that of the IMS framework (see figure below). Each SBC has a specific role:
1) Network Layer--Core security between networks and high availability
2) Media Layer--Media services and media interworking
3) Session Layer--Protocol Interworking, integration to applications and passing additional call data, and routing.
At each layer, the SBC is used for reporting and troubleshooting.
Trends that will continue to drive the SBC market include:
* 4G Cellular--Voice as VoIP/SIP and the desire to only transcode once for optimal quality, performance, and costs
* Peering--Bypassing IXCs and directly connecting the networks of each calling party
* Video--Providing co-browsing, pictures, and video from mobile devices into enterprises in conjunction with calls
* Multi-vendor--As Unified Communications applications grow, no single vendor will offer a complete solution
* International--Driving down the cost for international calling, especially with mobile devices
Organizations should invest time and effort in selecting their strategic SBC partner(s). The role of the SBC is growing, including the handling of all media services and interworking, which is the unique area of real-time communications that sets voice and video apart from every other IT application.
Sorell Slaymaker is VP-IT Communications Architecture, Unified IT Systems LLC. He blogs at No Jitter.
